Research Article: Do Decapod Crustaceans Have Nociceptors for Extreme pH?

Date Published: April 20, 2010

Publisher: Public Library of Science

Author(s): Sakshi Puri, Zen Faulkes, Michael N. Nitabach.

Abstract: Nociception is the physiological detection of noxious stimuli. Because of its obvious importance, nociception is expected to be widespread across animal taxa and to trigger robust behaviours reliably. Nociception in invertebrates, such as crustaceans, is poorly studied.

Three decapod crustacean species were tested for nociceptive behaviour: Louisiana red swamp crayfish (Procambarus clarkii), white shrimp (Litopenaeus setiferus), and grass shrimp (Palaemonetes sp.). Applying sodium hydroxide, hydrochloric acid, or benzocaine to the antennae caused no change in behaviour in the three species compared to controls. Animals did not groom the stimulated antenna, and there was no difference in movement of treated individuals and controls. Extracellular recordings of antennal nerves in P. clarkii revealed continual spontaneous activity, but no neurons that were reliably excited by the application of concentrated sodium hydroxide or hydrochloric acid.

Previously reported responses to extreme pH are either not consistently evoked across species or were mischaracterized as nociception. There was no behavioural or physiological evidence that the antennae contained specialized nociceptors that responded to pH.

Partial Text: Nociception is the physiological detection of stimuli that are potentially damaging to tissue [1]–[2]. It is closely correlated, but not identical, to the psychological experience of pain [3], and the relationship between nociception and pain, like any relationship between sensory information and subjective perception, is complex [4]–[5]. Understanding nociception in a particular species has significant implications for the care and welfare of that species, and may create new models for research on human pain. For example, a recent review [6] noted that nobody had yet recorded from mammalian sensory neurons for nociception at the receptor ending because the neurons are too small. Invertebrates may offer more tractable systems for studying nociceptor activation, as they have for other problems in neurobiology.

We found no behavioural or physiological evidence for nociceptors that respond to extreme pH in the antennae. Our results differ from those of Barr and colleagues [20], who reported a significant enhancement of antennal grooming with both benzocaine and weaker acids and bases than used here. We saw essentially no grooming in response to any stimuli.